1. Field of the Invention
This invention relates generally to prosthetic joints, and specifically to a prosthetic ankle which is inexpensive, durable, life-like in operation, and can be easily and inexpensively installed into rigid prosthetic leg devices.
2. Description of the Prior Art
The ankle portion of prosthetic devices for both below-knee and above-knee amputees is conventionally rigid. A piece of shock absorbing substance such as rubber may be provided at the heel of the artificial foot to both absorb shock during walking and to provide some flexibility. However, this construction is a poor substitute for the natural movement of an ankle. The natural rocking motion afforded by an ankle smooths the walking motion and the body parts associated therewith help to absorb the shock forces that are associated with walking.
Prosthetic ankles have been provided for the amputee which seek to simulate the movement of the human ankle. These are quite expensive and usually require the purchase of a new leg and foot as they are commonly designed to cooperate with the ankle. These devices typically provide only a limited range of mobility, on the order of 31/2.degree. forward of the vertical axis and 1.degree. backward. Previous ankle designs also provided little in the way of sideways give and therefore made walking laterally or sideways to an inclined surface difficult. Moreover, such designs often have no means for returning the foot to is natural position, perpendicular to the leg, without the application of external force. Those devices which do have internal biasing means are often either too restrictive and do not provide sufficient play or give, or are too loose and tend to flap about. Moreover, the biasing resistance which they provide is relatively constant over the full range of movement, limited though it is. It would be desirable to have more give at angles close to the vertical axis where fluctuations are common and more biasing at larger angles where greater support is needed. Previous prosthetic ankles have been very susceptible to wear and tend to work loose or deteriorate markedly with use. These failures of the prior art all contribute to a marked safety hazard in the use of prosthetic devices. Wobbling, and even falling, are everyday fears for the wearers of prosthetic leg devices.
The present invention provides a prosthetic ankle joint which is easily installed in conventional rigid prosthetic legs. The joint is inexpensively made and installed, and provides an extended range of movement, similar to that of the human ankle. The joint is internally biased to return the foot to a position perpendicular to the leg, and the biasing increases as bending increases. It is made of durable materials which can withstand the substantial forces which are placed on such a device.